The embodiments described herein relate generally to turbine components, and more particularly, to methods and systems for coupling a cover to the turbine component to facilitate medium flow along the turbine component.
In a gas turbine, hot gases flow along an annular hot gas path. Typically, turbine stages are disposed along the hot gas path such that the hot gases flow through buckets and nozzles of the turbine stages. The turbine buckets may be secured to a plurality of turbine wheels, with each turbine wheel being mounted to a rotor shaft for rotation therewith.
Conventionally, turbine buckets may include an airfoil extending radially outwardly from a substantially planar platform. A hollow shank portion extends radially inwardly from the planar platform and may include a dovetail or other means to secure the bucket to the turbine wheel. In general, during operation of the gas turbine, the hot gases are generally directed over and around the airfoil. To protect the airfoil from high temperatures, the airfoil may include an airfoil cooling circuit configured to supply a cooling medium, such as air, throughout the airfoil. The cooling circuit may reduce the temperature differential between the pressure and suction sides of the airfoil. In addition, the exterior surfaces of the airfoil may be coated with a thermal barrier coating to provide oxidation/corrosion and/or thermal protection. Theses coatings may be used in conjunction with a cooling scheme or arrangement for supplying air to the pressure side surface and/or the suction side surface of the airfoil.
The cooling circuit may use a series of film holes and/or channels defined through the airfoil. More particularly, the film holes are typically drilled through the airfoil surface typically at an angle and into the airfoil cooling circuit to allow the cooling medium flowing through the cooling circuit to be supplied to the airfoil surface. However, some film holes such as round holes, may provide for less than optimal cooling of the airfoil's surface. To improve cooling effectiveness, some airfoils may include advanced-shaped film holes (e.g., diffuser, chevron-shaped holes) or other complex-shaped outlets for the film holes. However, these advanced-shaped holes may be difficult to manufacture and, thus, significantly increase the overall costs of producing a turbine bucket. Moreover, some airfoils may include diffusers positioned on an outer surface of the airfoil and in flow communication with the film holes. Surface diffusers, however, can be difficult to manufacture, repair and/or replace.